Stannous fluoride has been shown to be an effective chemotherapeutic agent in combating tooth decay. While various mechanisms have been proposed to explain this anticavity action, only recently have we begun to learn what the actual products of the reaction between stannous fluoride and hydroxyapatite are. It is the objective of this project to extend the recent studies of this reaction system to low and high concentrations of stannous fluoride. In addition, the SnF2 - Ca(OH)2 - H3PO4 - H2O system will be studied. This system may provide a closer approximation to the oral environment than the stannous fluoride-apatite system does. The products of these reactions will be identified by application of x-ray diffraction, infrared, atomic absorption, and wet chemical analytical methods.